Rotary furnace for carburization

ABSTRACT

An improved furnace of the rotating type comprises a rod-shaped or tubular heating core of graphite or carbonaceous material fixedly arranged in the central portion of the furnace. A rotary cylinder having an inner wall of graphite or carbonaceous material is secured to rotate around the heating core. A casing is provided with means for rotatably holding the rotary cylinder, an opening for feeding a raw material, means for supplying electric power, an opening for discharging a product and a gas flow opening and is secured to hold an atmosphere of carburization inside the furnace.

United States Patent .1191

Hara et al.

[ 1 ROTARY FURNACE FOR CARBURIZATION [75] Inventors: Akio Hara; Masaya Miyake, both of ltami, Japan [73] Assignee: Sumitomo Electric Industries, Ltd.,

Higashi-ku, Osaka, Japan 22 Filed: on. 12, 1971 21 App1.N0.:l87,953

[30] Foreign Application Priority Data Oct. 30, 1970 Japan 1 45-95243 Sept. 16, 1971 Japan 46-71233 [52] U.S. Cl 23/279, 423/440, 432/114,

[51] Int. Cl. F27b 7/06, BOlj 6/00 [58] Field of Search 23/279, 227 R, 288 J; 263/32; 219/389; 13/20, 21, 35; 266/5 E, 18; 423/440, 441; 432/114 [561' References Cited UNlTED STATES PATENTS 3.350,495 10/1967 Barnes et al. 1 3 21 x [451 Apr. 9, 1974 1,700,942 2/1929 Lederer 13/20 3,111,394 11/1963 Weber et a1. 23/279 3,422,205 1/1969 Pisano et al. 13/35 Primary Examiner-James H. Tayman, Jr. Attorney, Agent, or Firm-Wenderoth, Lind & Ponack 5 7 ABSTRACT An improved furnace of the rotating type comprises a rod-shaped or tubular heating core of graphite or carbonaceous material fixedly arranged in the central portion of the furnace. A rotaryvcylinder having an inner wall of graphite or carbonaceous material is secured to rotate around the heating core. A casing is provided with means for rotatably holding the rotary cylinder, an opening for feeding a raw material, means for supplying electric power, an opening for discharging a product and a gas flow opening and is secured to hold an atmosphere of carburization inside the furnace.

9 Claims, 3 Drawing Figures mzmmun 9mm 3.802847 SHEET 1 BF 2 FIG. I

msmm m I 3302347 sum 2 m2 com OmnA

OOL-m1 BRIEF SUMMARY OF THE INVENTION This invention relates to a furnace for carburization, and more particularly it is concerned with a rotary furnace for carburization, which is suitable for the production of carbides of elements of Groups lV-A, V-A and VI-A of Periodic Table, actinide elements, boron and silicon.

Various attempts to produce carbides of the kind by gaseous ccmentation have hiterto been made, but have proven unsatisfactory on an industrial scale. Only the method has been put to practical use wherein a powdered metal or metal oxide is mixed with a carbonaceous powder such as carbon black by means of a ball mill and, optionally after formed into a certain size by a press, the mixture is then charged in a graphite boat and heated in hydrogen or in vacuum. However, there is no choice but to do employ batch production by use of this method. Furthermore, this method has a disadvantage that, since the reaction of forming these carbides is accompanied by the generation of heat, an abnormal generation of heat takes place in the lower portion of the boat, resulting in a localized grain growth, and the degree of cementation differs between the upper portion and lower portion of the boat in the carburization in hydrogen, being accompanied by cementation, resulting in unevenness of the quantity of carbon combined. In order to solve this disadvantage, it is necessary to advance the reaction in a continuous manner with agitation of the reactants.

To this end, the use of rotary furnaces is recommended, but those used in the cement manufacturing industry or for the hydrogen reduction of tungsten oxide cannot resist high temperatures such as required for the production of the foregoing carbides. There is nothing but carbon as a material for the rotating tube used in a protective atmosphere such as hydrogen gas at a high temperature of up to 2,000C. Carbon materials, however, are porous so that leakage of hydrogen gas occurs as a troublesome problem. The heating system of carbon materials, in addition, requires a large electric current and large slidable contacts. Therefore, rotation of the furnace itself is very difficult. Since carbon has such a high thermal conductivity that, when the temperature of the central portion of a carbon tube is raised to 800-2,200C, the end portion thereof will also be of a high temperature, and even bearings in the furnace system have to be resistant to high temperatures.

It is an object of the present invention to provide a rotary furnace for carburization, whereby the above mentioned disadvantages of the prior art are overcome.

It is another object of the invention to provide a rotary furnace for carburization, whereby carbides with -a uniform composition and very narrow grain size dis- BRIEF DESCRIPTION OF THE DRAWING The accompanying drawings are to illustrate the principle and merits of the invention in more detail.

FIG. 1 shows schematically one form of the rotary furnace for carburization according to the invention.

FIG. 2.shows a cross sectional view of the furnace of 7 FIG. 1 at the central portion thereof.

Located at the center of furnace body 18 is heating core 1, around which rotating cylinderv 10 and fixed cylinder 11 are arranged.

FIG. 3 shows a dispersion of the quantity of carbon in tungsten carbide powder carburized by the prior art furnace.

DETAILED DESCRIPTION OF THE INVENTION It has been found as a result of various studies that the foregoing objects can be accomplished by providing a fixed, rod-shaped or tubular heating core of graphite or carbonaceous material in the center of a furnace for carburization and arranging a rotating cylinder having a graphite or carbonaceous material inner surface coaxially around such heating core.

That is to say, there is the provision of a rotary furnace for carburization, which comprises a rod-shaped or tubular heating core of graphite or carbonaceous material fixedly positioned in the central portion of the furnace, a rotary cylinder having an inner wall of graphite or carbonaceous material and positioned to rotate coaxially around the heating core, and a casing provided with means for rotatably supporting the rotary cylinder, an opening for feeding a raw material, means for supplying electric power, an opening for discharging a product and a gas flow opening and being constructed to maintain an atmosphere of carburization within the furnace. The most important aspect of this furnace lies in that rotation of the rotary cylinder is independent of the fixed heating core and, consequently, sliding electrical contacts are unnecessary. Since the furnace'is of an internal heating type, an outer wall for shielding hydrogen gas can be kept at normal temperature by inserting a heat insulating mate rial between the inner and outer walls, and the problems of insulating materials can thus be solved.

In accordance with the second feature of the invention, the rotating cylinder is modified into a double structure of a rotating cylinder and fixed cylinder. In this case, the fumace comprises a rod-shaped or tubular heating core of graphite or carbonaceous material fixedly positioned in the central portion of the furnace, a rotary cylinder having an inner wall of graphite or carbonaceous material and positioned to rotate coaxially around the heating core, a fixed cylinder fixedly positioned to surround the rotary cylinder, and a casing provided with means for rotatably supporting the rotary cylinder, means for fixedly supporting the fixed cylinder, an opening for feeding a raw material, means for supplying electric power, an opening for discharging a product, a gas flow opening, and being constructed to maintain an atmosphere of carburization with the furnace.

By these carburizing furnaces, carbides of high melting point metals such as tungsten, titanium, tantalum, columbium, hafnium, zirconium, vanadium, chromium and molybdenum having a substantially stoichiometric amount of combined carbon and a very narrow grain size distribution are economically produced from the high melting point metals or oxides thereof. The features and merits of these furnaces are summarized below:

1. Since rotation of the rotary section is independent of the fixed heating core, slidable contacts for supplying electric power are not necessary.

2. Since the furnace is of the internal heating type with a heating core provided therein, it is relatively easy to maintain high temperatures, the raw material is directly exposed to the heat radiation from the heating core, and the furnace can be adapted for the continuous production of hard carbides without the us e of expensive heat insulating materials.

3. Since the heating core is fixedly arranged in the central portion of the furnace, the thermal efficiency is raised and a large electric current can be supplied independently of the rotating mechanism of the cylinder.

4. Since the cylinder is of a double structure of a rotary cylinder and fixed cylinder, rotation of the cylinder can smoothly be effected, and accordingly, feeding of powdered raw materials can be carried out corresponding to movement of the powder in the cylinder. Moreover, leakage of hydrogen gas can be prevented.

5. Since the cylinder is of a double structure, the furnace structure is so simple that the driving mechanism is composed of shafts only.

Reactants fed into the rotary furnace of the invention flow down between the inner wall and the heating core little by little in the form of powder or granules. The diameter of the heating core and the inner diameter of the rotary cylinder may be varied with the quantity of reactants and reaction temperature. When it is further desired to increase the surface area of the heating core, it may be tubular shaped. Moreover, the inclination of the furnace body may be varied depending on the desired reaction speed The invention is fuither illustrated in the accompanying drawings. With particular reference to FIG. 1, carbon heating core 1 is fixed by copper electrode 2 and furnished with a large electric current through bus bar 3, which is fixed by insulator 4 and supported by metal fitting 5. Copper electrode 2 is cooled by water supplied by conduit 8. Rotary cylinder or tube is located coaxially around heating core 1 and rotated within and in'contact with fixed cylinder or tube 1 1 and carbon ring 12. That is to say, rotary cylinder or tube.

10 is set by carbon ring 12 and moved in fixed cylinder or tube 11. Fixed cylinder or tube 11 is positioned in the center of the furnace by carbon disk 13. The driving mechanism of rotary cylinder 10 consists of stainless steel gears 14 supported by carbon bearings 15 and shafts 17 in gear box 16, the driving being effected through shafts 17. The above mentioned mechanism is enclosed in furnace body or casing 18. The space between fixed cylinder ll and furnace body 18 is filled with heat insulating material 19 so that the temperature of the central portion may be raised up to 2,200C. l-Iydrogen gas enters hydrogen inlet 20 and leaves from hydrogen outlet 21. Teflon 22 is used for the purpose of insulation and preventing leakage of hydrogen from around bus bar 3. Furnace body 18 is provided with cooling water tube 23 on the outer surface thereof to prevent it from overheating.

Referring to FIG. 2, carbon tube pyrometer 31 for measurement of the outer surface temperature of rotary cylinder 10 is positioned to extend through furnace body 18 and fixed cylinder 11. Furnace body 18 is mounted on support frame 32 in such a manner that its inclination may be varied in accordance with the desired reaction speed.

In operation of this furnace for carburization, a raw material powder is charged in hopper 24 from a feed opening (not shown) of hopper cover 25 and moved downwardly by screw 26 upon rotation of shaft 27.

Then the raw material powder is fed to rotary cylinder EXAMPLE 1 Using a rotary furnace of the invention (having no fixed cylinder), tungsten carbide was produced by the following condition:

Inner diameter of rotary cylinder (graphite tube) Outer diameter of heating core 30 mm (carbon) Wholc length of rotating part 2 m Inclination of furnace body 4 Rotation Speed 6 rpm Flow rate of hydrogen I0 I/min Electric power 20 KW A mixed powder of tungsten and carbon was pressed in a mold and crushed, and the resulting granule was continuously fed, while keeping the furnace at 1,450C over about 60 cm, thus obtaining continuously tungsten carbide with a uniform property at a rate of 8 kg/hour.

EXAMPLE 2 Tungsten powder of 0.711. was mixed with 6.25 of carbon powder in a ball mill and the granulated powder having a grain size distribution of 1 mm to 0.02 mm was obtained. The resulting granulated powder was subjected to carburization reaction by the use of a rotary v furnace for carburization according to the invention as shown in FIGS. 1 and 2, to obtain WC powder. The various conditions of the furnace are as follows:

Inner diameter of rotary cylinder 60 mmda Outer diameter of heating core 20 mm Whole length of rotating part I500 mm Inclination of furnace body 4 Rotation speed 2 rpm Flow rate of hydrogen I5 I/min Electric power 10 KW Carburization temperature I400 C The granulated powder was fed in the hopper and moved at a rate of 5 kg/hr continuously in the cylinder. The reaction proceeded smoothly and the product was discharged as WC powder without adhesion to the inner wall of the cylinder. No troubles occurred when '1 ton of the product was produced.

In the case of carrying out th e reaction using a carbon case in a horizontal Tammann furnace according to the carburization method of the prior art, there occurred a dispersion of the quantity of carbon depending on the position in the boat, as shown in FIG. 3. When the position in the carbon case was numbered to the flow of hydrogen gas as follows:

Front upper 1 Center upper 4 Back upper 7 middle 2 middle 5 middle 8 lower 3 lower 6 lower 9 the quantity of carbon by weight) in the each position was as tabulated below.

When carburization was continuously carried out using the furnace of the invention, on the other hand, the fluctuation of carbon quantity was much reduced as shown in Table l.-

Dispersion of carbon quantity of WC power in rotary furnace for carburization TC (Total Carbon) PC (Free Carbon) \lChMbUDN- Note: Sampling was carried out every 15 minutes. EXAMPLE 3 the following conditions:

inner diameter of rotary cylinder 80 mm4 Outer diameter of heating core 20 mmda,

rod-shaped Inclination of furnace body 6 Rotation speed of rotary cylinder 2 rpm Flow rate of hydrogen gas l0 l/min Electric power 12 KW Carburization temperature 1500 C The reactants were fed to the furnace body from. the hopper at a rate of kg/hr. The so obtained WC powder had a total quantity of carbon of 6.19 and free carbon of 0.06 and the grain size distribution was much better than in the case of using a carburizingfurnace of the prior art. I

To this WC powder was added 7 of cobalt powder and mixed with acetone for 100 hours in a ball mill having an inner diameter of 200 mmqb and cylinder length of 270 mm, followed by drying by heating at 100 C.

Note:

86 specific gravity H Rockwell hardness, A scale Hy Vickers hardness TRS transverse rupture strength 41m saturated magnetisation quantity H coercive force From the WC powder produced by the prior art method and from the WC powder produced by means of the carburizing furnace of the invention alloys were respectively prepared and compared regarding their properties. The latter is favourably compared with the former in the fact that the grain size distribution of WC in the alloy is better, abnormally grown WC crystals are less and the transverse rupture strength is higher.

EXAMELE 4 inner diameter of rotary cylinder 80 mm Outer diameter of heating core 20 mmdz Inclination of furnace body 4 Rotation speed of rotary cylinder 2 rpm Flow rate of hydrogen l0 l/min Electric power 18 KW Carburization temperature The reactants were fed to the furnace from the hopper at a rate of 10 kg/hr. The so obtained WC powder had a total carbon quantity of 6.23 and free carbon quantity of 0.10 and the grain size distribution was much better than in the case of using a carburizing furnace of the prior art.

To this WC powder was added 10 of cobalt powder and mixed with acetone for'80 hours in a ball mill having an inner diameter of 200 mm and cylindrical length of 250 mm, followed by drying by heating at 100 C. The resulting mixed powder was pressed in a mold under a pressure of l ton/cm and sintered at 1,450 C fonl hour in vacuum. The mechanical properties of the resulting alloy are shown in Table 3.

TAB LE 3 H, H" TRS 417:! H WC powder of the invention V1.60 87.0 l 100 300 W6 WC powder of the prior art |4.6() 86.5 M 270 I 65 The resulting mixed powder was pressed in a mold under a pressure of l ton/cm and sintered at 1,450 C for 1 hour in vacuum. The mechanical properties of the 'esultingalloy are shown in Table 2:

TABLE SG H H TRS 4710- H WC powder of the invention 14.90 91.2 1500 210 I40 I65 WC powder of the prior art 14.87 91.0 1475 l70 I60 3,802,847 7 8 properties. The latter is favourably compared with the controlled powder having a grain size distribution that former in the fact that the grain size distribution of WC 80 consists of 10 meshes to 20 meshes. The thus sizein the alloy is better, abnormally grown WC crystals controlled powder was reacted at 1,200 C in H are less and the transverse rupture strength is higher. atmosphere by means of the furnace as shown in Example 2. Feeding of the powder was carried out in such EXAMPLE 5 a manner that the thickness thereof did not exceed 5 Tungsten oxide (W0 powder of 0.21.4. was mixed mm in the cylinder. A TiC powder with a combined with 16 by weight of carbon powder and 2 by carbon of 19.5 was obtained without explosive reacweight of stearic acid in a ball mill, pressed in a mold tion ina yield of 98 under a pressure of 1 ton/cm and then crushed to give a powder having a grain size distribution of 2 mm to 0.2 Th h b i d Tic powder was i d i h 10 mm- The resulting Powder was jecte to calbullzvar of nickel powder and 10 of molybdenum powder for tion in two steps by the use Of the rotary Car g 10 hours by means of a vibrating mill using balls each furnace of the invention. The first step was carried out having a diameter of 10 mm and being a cermet ball at 1,400 C in nitrogen and the second step, at 1,800 and alcohol in an amount of two times the powder. The "C in hydrogen. Various conditions of the furnace are mixed powder was pressed under a pressure of 2 shown in Table 4. tons/cm and sintered at 1,375 C for 1 hour in a vac- TAB LE 4 First step Second step carburization carburization Inner diameter of 60 mmqS 80 mm rotary cylinder Heating core rod-shaped tubular heating core heating core Dimension of heating mm X 1700 mm X 20mm X 1700 core Inclination of furnace 6 4 Rotation speed 4 rpm 2 rpm Atmosphere N l-l Carburizution temperature 1400 C I800 The WC powder had a total carbon quantity of 6.32 uum having a degree of vacuum of 2 X 10 to obtain and free carbon quantity of 0.20 and a grain size of an alloy having the following characters:

E AMPLE 6 X TAB LE 6 Hafntum oxide (Hf O powder of 0.2g was mixed with 15 by weight of carbon powder and 2 by v 5G H Hy i 41m weight of stearic' acid in a ball mill, pressed under a 5.55 91.9 1570 170 60 pressure of 1 ton/cm and then crushed to obtain a powder having a grain size of 1 mm to 0.1 mm.'The thus size-controlled powder was subjected to carburiza- EXAMPLE 8 tion in two steps using the rotary furnace of the inven- 7 tion. The first step was carried out at 1,600 "C in argon and the second step, at 1,900 C in hydrogen. Various 45 52 of tungsten powder of 1p. and 30 of titanium conditions of the furnace are shown in Table 5. dioxide (TiO powder of 0.2;1. were mixed with 18 TABLE5 First step Second step carburization carburization Inner diameter of mm 80 mm rotary cylinder Heating core rod-shaped tubular heating core heating core Inclination of furnace 6 4 Rotation speed 4 rpm 2 rpm Atmosphere Ar 2 Carburization temperature 1600 C 1900 C The HfC powder had a total carbon quantity of 6.44 of carbon powder and 2 of stearic-acid for 1 hour by and free carbon quantity of 0.20 and a grain size of 60 the use of a high speed mixer; The mixture was pressed lg. by a powder roller and passed through a sieve to obtain a size-controlled powder having a grain size distribu- EXAMPLE 7 tion of 1.0 mm to 0.1 mm. The resulting size-controlled Titanium hydride (TiH powder was mixed with 21 powder was reacted at 2,000 C in hydrogen using the of carbon and 5 of stearic acid for 20 hours in a rotary furnace of the invention under the following ba11mi11, pressed in a mold and crushed to obtain a sizeconditions:

' granulated by a pan type granulator while spreading ac- .nlaBt 7 lnner diameter of rotary cylinder I50 mmd Heating core tubular, outer diameter 50 mmdB inner diameter mmd: Whole length of rotating part 3 m Inclination of furnace body 8 Rotation Speed of cylinder 6 rpm Carburization temperature 1900 "C Electric power 30 KW Using the above mentioned furnace, a solid solution of 10 EXAMPLE 10 (W.Ti)C was produced at a rate of 20 kg/hr, having the following composition.

-.....,.TAB E l rc FC cc 0 H N,- 9.s0 7. 0.02 7. 9.78 0.02 0.0003 0.0002

From the resulting solid solution (W.Ti)C and WC The foregoing composition was ball-milled for 100 hours and sintered by holding at 1,450 C for 1 hour in a high vacuum furnace. At the same time, another cemented carbide was prepared from WC and (W.Ti)C solid solution type carbide obtained by the prior art method. Comparison of their cutting properties was carried out by the following cutting test:

workpiece Cr-Mo steel, hardness H 250 Cutting speed 110 m/min, feed 0.54 r'nm/rev, depth of cut 2 mm As a result of this test it was found that our cemented 0 carbide had a life of about 1.3 times as long as the comparative cemented carbide, such life being that continued until the Flank wear reached 0.3 mm

EXAMPLE 9 30 of tungsten powder, 22 of tantalum oxide (Ta O powder and 30 of titanium dioxide (TiO powder were mixed with 18 of carbon powder for 1 hour by means of a high speed mixer. The mixture was etone thereon. The thus granulated powder was subjected to carburization under the following conditions:

Inner diameter of rotary cylinder Heating core Inclination of furnace body 150 mm 8O mm b X mm X 2500 10 Rotation speed 2.5 rpm Flow rate of hydrogen 20 l/min Carburization temperature 1900 "C 60 The granulated powder was fed to the furnace in such Chromium oxide (Cr O powder was mixed with 26 of carbon powder and 2 of stearic acid in a ball mill, pressed under a pressure of 1 ton/cm and crushed 5 to obtain a powder having a grain size distribution of 2 mm to 0.2 mm. The thus size-controlled powder was subjected to carburization by the rotary furnace of the invention at 1,500 C in hydrogen. The conditions of the furnace are as follows:

lnner diameter of rotary cylinder mm Outer diameter of heating core 20 mm Inclination of fumace body 6 Rotation speed 2 rpm Flow rate of hydrogen 10 l/min Electric power 12 KW Carburization temperature H,, 1500 "C Thus a Cr O powder with a quantity of carbon combined of 12 was given.

EXAMPLE 1 1 Inner diameter of rotary cylinder Heating core Inclination of furnace body 80 mm4 rod shaped, 20 mm 4 o Rotation speed 1 rpm Flow rate of hydrogen 5 l/min Whole length of rotating part 3 m The furnace, yielding the product at a rate of 5 kg/hr, was fit for use as a rotary furnace on a commercial scale.

EXAMPLE 12 Tantalum oxide (Ta O powder and 16 of powder were ball-milled, pressed and crushed to obtain a controlled grain size. The resulting powder was heated at 1,700 C in hydrogen by the use of the rotary furnace of the invention to give a TaC powder with a theoretical amount of combined carbon,-TC 6.30 and FC 0.1 1 The conditions of the furnace are as follows:

Inner diameter of rotary cylinder Heating core Inclination of furnace body 7 80 mmda rod-shaped, 20 mm 6 a Rotation speed 2 rpm Flow rate of hydrogen 5 l/min Whole length of rotating part 3 m The furnace, yielding the product at a rate of 5 kg/hr, was fit for use as a rotary furnace on a commercial scale.

EXAMPLE 13 Vanadium oxide (V 0 powder and 29 carbon powder were ball-milled, pressed and crushed to obtain a controlled grain size. The resulting powder was a l 1 heated at 2,100 "C in hydrogen by the use of the rotary carburizing furnace to give a V C powder with a theoretical amount of carbon, TC 19.00 and FC 4.02 The conditions of the furnace are as follows:

80 mmzb inner diameter of rotary cylinder tubular, 3O mm 4 Heating core Inclination of furnace body Rotation speed 2 rpm Flow rate of hydrogen l/min Whole length of rotating part 3 rn The furnace, yielding the product at a rate of 3 kg/hr, was fit for use as a rotary furnace on a commercial Scale.

EXAMPLE 14 and FC 0.20 The conditions of the furnace are as follows:

' 100 mmda lnner diameter of rotary cylinder tubular, 40 mmrb 4 0 Heating core Inclination of furnace body Rotation speed 3 rpm Flow rate of nitrogen 5 l/min Whole length of rotating part 3 m The furnace, yielding the product at a rate of 7 kg/hr, was fit for use as a rotary furnace on a commercial scale.

What is claimed is: 1. A rotary furnace for carburization which comprises:

an enclosing casing constructed to maintain a carburization atmosphere within said furnace, said casing having an opening at the upper portion thereof for feeding a solid raw material therein, an opening at the lower portion thereof for discharging a carburized product therefrom, a gas feed inlet, a gas exhaust outlet, and being inclineable to provide a downward slope thereof; a raw material feeding means communicating with said upper opening; a product collecting means communicating with said lower opening; I a rotary hollow cylinder of graphite or carbonaceous material having a large ratio of length to diameter, tubular supporting member means of graphite or carbonaceous material arranged in said enclosing casing, said rotary hollow cylinder being rotatably mounted on said supporting member means and having means to receive said raw material from said raw material feeding means and to discharge said carburized product to said product collecting means; an elongated heating core of graphite or carbonaceous material fixedly positioned substantially coaxially at the center of said rotary cylinder;

means for supplying electric power to said heating core and connected with the end of said heating core; I

drive means for rotating said rotary hollow cylinder;

and

a heat insulating material arranged round said rotary hollow cylinder independently of the rotation thereof.

2. The rotary furnace according to claim I, wherein said supporting member means is a fixed hollow cylinder of graphite or carbonaceous material having a slightly larger diameter than said rotary hollow cylinder, the inner periphery of said fixed hollow cylinder being in contact with the outer periphery of said rotary hollow cylinder, and said fixed hollow cylinder being fixed to said enclosing casing.

. 3. The rotary furnace according to claim 2, wherein said rotary and fixed hollow cylinders have holes therein, and said raw material is fed to said rotary hollow cylinder when said holes coincide- 4. The rotary furnace according to claim 2, wherein said fixed hollow cylinder is fixed to said enclosing casing by means of a carbon disk.

5. The rotary furnace according to claim 1, wherein said gas feed inlet is provided at the product discharge end of said casing, and said gas exhaust outlet is provided at the raw material feed end of said casing.

6. The rotary furnace according to claim 1, wherein said raw material feeding means is a vertical screw feed device.

7. The rotary furnace according to claim 1, wherein said electric power supplying means is a bus bar fixed by an insulator and supported by a metal fitting.

8. The rotary furnace according to claim 1, wherein said drive means comprises a gear mechanism.

9. The rotary furnace according to claim 8, wherein said gear mechanism comprises a plurality of gears and shafts supported by carbon bearings, one of said shafts being air-tightly connected to a power source outside said enclosing casing. 

2. The rotary furnace according to claim 1, wherein said supporting member means is a fixed hollow cylinder of graphite or carbonaceous material having a slightly larger diameter than said rotary hollow cylinder, the inner periphery of said fixed hollow cylinder being in contact with the outer periphery of said rotary hollow cylinder, and said fixed hollow cylinder being fixed to said enclosing casing.
 3. The rotary furnace according to claim 2, wherein said rotary and fixed hollow cylinders have holes therein, and said raw material is fed to said rotary hollow cylinder when said holes coincide.
 4. The rotary furnace according to claim 2, wherein said fixed hollow cylinder is fixed to said enclosing casing by means of a carbon disk.
 5. The rotary furnace according to claim 1, wherein said gas feed inlet is provided at the product discharge end of said casing, and said gas exhaust outlet is provided at the raw material feed end of said casing.
 6. The rotary furnace according to claim 1, wherein said raw material feeding means is a vertical screw feed device.
 7. The rotary furnace according to claim 1, wherein said electric power supplying means is a bus bar fixed by an insulator and supported by a metal fitting.
 8. The rotary furnace according to claim 1, wherein said drive means comprises a gear mechanism.
 9. The rotary furnace according to claim 8, wherein said gear mechanism comprises a plurality of gears and shafts supported by carbon bearings, one of said shafts being air-tightly connected to a power source outside said enclosing casing. 